Impeller wheel

ABSTRACT

The present invention relates to a pump impeller ( 12 ) of a centrifugal or half axial type to be used in a pump for pumping liquids, wherein the impeller is arranged with one or several vanes ( 18 ), that the vanes are attached to cover discs ( 12, 16 ) on each side, forming a so called closed impeller wheel, characterized in that the leading edges ( 40 ) of the vanes are swept backwards at the inlet opening ( 42 ) in one of the cover discs ( 16 ) of the impeller.

TECHNICAL FIELD

The invention concerns a pump impeller and more precisely a pumpimpeller for centrifugal-or half axial pumps for pumping of fluidscontaining pollutants.

BACKGROUND OF THE INVENTION

In literature there are lot of types of pumps and pump impellers forthis purpose described, all however having certain disadvantages. Aboveall, this concerns problems with wear, clogging and low efficiency.

Sewage water contains a lot of different types of pollutants, the amountand structure of which depend on the season and type of area from whichthe water emanates. In cities plastic material, hygiene articles,textile etc are common, while industrial areas may produce wearingparticles. Experience shows that the worst problems are rags and thelike which stick to the leading edges of the vanes and become woundaround the impeller hub. Such incidents cause frequent service intervalsand a reduced efficiency.

In agriculture and pulp industry different kinds of special pumps areused, which should manage straw, grass, leaves and other types oforganic material. For this purpose the leading edges of the vanes areswept backwards in order to cause the pollutants to be fed outwards tothe periphery instead of getting stuck to the edges.

Different types of disintegration means are often used for cutting thematerial and making the flow more easily. Examples are shown in SE-435952, SE-375 831 and U.S. Pat. No. 4,347,035.

In literature the designs of the pump impellers are described verygenerally, especially as regards the sweep of the leading edges of openimpeller wheels. Attempts to define the sweep of the leading edges foran open impeller wheel are described in e.g. EP 0916851 and EP 0916852.

During pumping where high lifting heights are required, for example inmines, closed pump impellers are often used, i.e. such with two coverdiscs, an upper and a lower as well as intermediate vanes, because thesetypes of impellers reduce the axial load on the pump in comparison tothe open type impellers. On the other hand, closed impellers have alesser lead-through, which means higher risk for clogging.

EP 0395604 discloses an impeller wheel, which is arranged with one orseveral vanes that are attached to cover discs on each side forming a socalled closed impeller wheel. The leading edges of the vanes are placedgenerally in a plane perpendicular to the axis of rotation of theimpeller, at the inlet opening in one of the cover discs.

Regarding closed impeller wheels they are generally designed withleading edges placed in the central inlet such that they are ratherstraight as seen in the flow direction. It has been found that duringuse, and in particular when the liquid contains rather large quantitiesof abrasive pollution, there is considerable wear on the leading edgesof the vanes. There is further a risk that pollutants such as rags,plastic bags and other elongated objects get stuck on the leading edges,thereby requiring cleaning of the pump.

BRIEF DESCRIPTION OF THE INVENTION

The aim of the present invention is to remedy the above mentionedproblems and in particular in connection with closed impeller wheels.

This aim is solved according to a main aspect of the invention by whatis characterized in claim 1. Preferable embodiments of the inventionform the dependent claims.

According to a main aspect of the invention, it is characterized by animpeller wheel of a centrifugal or half axial type to be used in a pumpfor pumping liquids, wherein the impeller is arranged with one orseveral vanes, that the vanes are attached to cover discs on each side,forming a so called closed impeller wheel, characterized in that theleading edges of the vanes are swept backwards at the inlet opening inone of the cover discs of the impeller.

According to a further aspect of the invention, it is characterized inthat the leading edges co-operate with cutting means arranged in acentral inlet opening of the pump,

Preferably the leading edges protrude somewhat out of the inlet opening,and that the cutting means constitute at least one narrowing section ofthe gap between the central inlet opening of the pump and the leadingledges of the impeller, whereby, when the leading edges sweep past thesesections during operation, a cutting action is obtained there between.

By designing the leading edges of the vanes strongly backswept it hasbeen found that the wear on these edges are reduced drastically. Thedesign also reduces the risk of material getting stuck on the edges.Rather such material are fed towards the periphery.

The material that however tends to get stuck on the edges at the inletopening of the impeller will be cut by the cutting means. In a preferredembodiment the leading edge of the vanes co-operate with two narrowingparts of the inlet opening of the pump housing.

For a good performance regarding the pump function and transportation ofmaterial towards the periphery, the sweep angle α should be in theregion 40-60° and the sweeping of the leading edges may generally followthe curvature of a logarithmic spiral.

In all an impeller wheel with improved performance and wear resistanceis obtained, leading to long operation cycles between maintenance andservice.

These and other aspects of and advantages with the present inventionwill become apparent from the following detailed description and fromthe drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following detailed description of the invention, reference willbe made to the drawings, of which

FIG. 1 is an axial cross-section through a pump according to theinvention,

FIG. 2 a is a perspective view from above of an impeller wheelcomprising the present invention,

FIG. 2 b is a view corresponding to FIG. 2 a from below,

FIG. 3 is a view from below of the impeller wheel of FIG. 2, and

FIG. 4 is a bottom plate to be mounted in a pump and co-operating withthe impeller wheel according to FIG. 1.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows an impeller wheel of the closed type mounted in a pumpcomprising a drive shaft 10 connected to an electrical motor (not shown)for driving the pump. To the lower end of the shaft a pump impeller 12is mounted, comprising upper 14 and lower 16 cover discs, vanes 18 andback vanes 19. The above mentioned components are mounted in a pumphousing 20, having a bottom wall 22, an inlet 24 and an outlet 26. Thepump impeller 12 is mounted such in the pump housing that there is a gap28 between the peripheral surface of the lower cover disc 16 and aninner side wall of the pump housing 20, a space 29 between the lowerdisc and the bottom wall as well as a gap 30 between a lower surface ofthe lower cover disc 16 and an upper surface of the bottom wall 22.

According to the principles for a centrifugal pump, the liquid is suckedin axially through the inlet 24 and leaves the pump through the outlet26 according to flow arrows A, B and C.

According to the present invention the vanes 18 are designed such thatthe leading edges 40 are swept strongly backwards at the inlet opening42 of the impeller wheel, in relation to the direction of rotation R.The sweep angle could be increased from the hub and outwards. The sweepof the leading edges could be defined by a logarithmic spiral where thesweep angle α is π/2−β, where β is the angle of the logarithmic spiral.Preferably the sweep angle should be in the region 40-60°.

At the inlet opening of the impeller the leading edges are placedgenerally in a plane perpendicular to the axis of rotation 10 of theimpeller. The advantage with this design is to make sure that pollutantsslide towards the periphery instead of getting stuck on the edges. Ithas further been shown that the wear on the leading edges are reducedwhen they have this configuration instead of the conventional design.

Further, the leading edges protrude somewhat out of the central openingof the impeller, FIG. 1. The edge parts 44 of the vanes protruding abovethe bottom surface of the lower cover disc 16 can be arranged toco-operate with the edge part 46 of the stationary inlet 24 of thehousing arranged in a bottom plate 22. The circular inlet is thusarranged with two oppositely arranged straight parts 50 whereby the gapbetween the vanes and the edge part of the inlet becomes very small.Elongated pollution such as rags, plastic bags and the like that havebeen stuck on the leading edges of the vanes will be cut here.

In total the design of the leading edges being swept and protrudingsomewhat, and co-operating with the opening of the bottom plate, greatlyreduces the risk of pollutants getting stuck and reduces the wear on theleading edges.

It is to be understood that the embodiment described above and shown inthe drawings is to be regarded as a non-limiting example of theinvention and that it may be modified within the scope of the patentclaims.

1. An impeller wheel (12) of a centrifugal or half axial type to be usedin a pump for pumping liquids, wherein the impeller (12) is arrangedwith one or several vanes (18), that the vanes (18) are attached tocover discs (14, 16) on each side, forming a so called closed impellerwheel, that the leading edges (40) of the vanes (18) are placedgenerally in a plane perpendicular to the axis of rotation (10) of theimpeller (12), at the inlet opening (42) in one of the cover discs (16),characterized in that the leading edges (40) of the vanes (18) are sweptbackwards at the inlet opening (42) in one of the cover discs (16) ofthe impeller in relation to the direction of rotation (R).
 2. Impellerwheel according to claim 1, wherein the leading edges (44) protrudesomewhat out of the inlet opening (42), arranged and capable ofco-operating with cutting means (50) arranged in a central inlet openingof the pump.
 3. Impeller wheel according to claim 2, wherein the cuttingmeans constitute at least one narrowing section of the gap between thecentral inlet opening of the pump and the leading ledges (40) of theimpeller.
 4. Impeller wheel according to claim 1, wherein the leadingedges (40) are swept generally corresponding to a logarithmic spiral. 5.Impeller wheel according to claim 4, wherein a sweep angle (α) of theleading edges (40) is Π/2−β, where β is the angle of the logarithmicspiral.
 6. Impeller wheel according to claim 1, wherein the sweep angle(α) of the leading edges (40) are in the region 40-60°.
 7. Pumpcomprising an impeller wheel according to claim 1.